Printhead assembly with ink pump and shut off valve

ABSTRACT

A printhead assembly for engagement with an ink supply ( 112 ), a printhead integrated circuit (IC) ( 74 ) in fluid communication with the ink supply via an upstream ink line ( 67 ), the printhead IC ( 74 ), a waste ink outlet in fluid communication with the printhead IC ( 74 ) via a downstream ink line ( 106 ), an upstream shut off valve ( 138 ) in the upstream ink line ( 67 ), and, a downstream pump mechanism ( 114 ) in the downstream ink line. With a valve upstream of the printhead and a pump downstream of the printhead, the user has active control of the ink flow upstream, downstream or in the printhead IC. In the event that problems such as ink flooding, color mixing or printhead depriming occur, the user can follow simple troubleshooting protocols to rectify the situation.

FIELD OF THE INVENTION

The present invention relates to the field of printing and in particularinkjet printing.

COPENDING

The following applications have been filed by the Applicantsimultaneously with the present application:

-   -   SBF006US SBF008US

The disclosures of these co-pending applications are incorporated hereinby reference. The above applications have been identified by theirfiling docket number, which will be substituted with the correspondingapplication number, once assigned.

CROSS REFERENCES

The following patents or patent applications filed by the applicant orassignee of the present invention are hereby incorporated bycross-reference.

09/575197 7079712 09/575123 6825945 09/575165 6813039 6987506 70387976980318 6816274 7102772 09/575186 6681045 6728000 7173722 708845909/575181 7068382 7062651 6789194 6789191 6644642 6502614 66229996669385 6549935 6987573 6727996 6591884 6439706 6760119 09/5751986290349 6428155 6785016 6870966 6822639 6737591 7055739 09/5751296830196 6832717 6957768 09/575162 09/575172 7170499 7106888 71232396405055 6628430 7136186 10/920372 7145689 7130075 7081974 10/91924210/919243 7161715 7154632 7158258 7148993 7075684 11/635526 11/65054511/653241 11/653240 10/503924 7108437 6915140 6999206 7136198 70921307170652 6967750 6995876 7099051 11/107942 11/107943 11/209711 11/5993367095533 6914686 7161709 7099033 11/124158 11/124196 11/124199 11/12416211/124202 11/124197 11/124154 11/124198 11/124153 11/124151 11/12416011/124192 11/124175 11/124163 11/124149 11/124152 11/124173 11/12415511/124157 11/124174 11/124194 11/124164 11/124200 11/124195 11/12416611/124150 11/124172 11/124165 11/124186 11/124185 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11/495818 11/495819 11/482978 11/64035611/640357 11/640358 11/640359 11/640360 11/640355

BACKGROUND OF THE INVENTION

Inkjet printing is a popular and versatile form of print imaging. TheAssignee has developed printers that eject ink through MEMS printheadIC's. These printhead IC's (integrated circuits) are formed usinglithographic etching and deposition techniques used for semiconductorfabrication.

The micro-scale nozzle structures in MEMS printhead IC's allow a highnozzle density (nozzles per unit of IC surface area), high printresolutions, low power consumption, self cooling operation and thereforehigh print speeds. Such printheads are described in detail in U.S. Ser.No. 10/160,273 (MJ40US) and U.S. Ser. No. 10/728,804 (MTB001US) to thepresent Assignee. The disclosures of these documents are incorporatedherein by reference.

The small nozzle structures and high nozzle densities can createdifficulties with nozzle clogging, de-priming, nozzle drying (decap),color mixing, nozzle flooding, bubble contamination in the ink streamand so on. Each of these issues can produce artifacts that aredetrimental to the print quality. The component parts of the printer aredesigned to minimize the risk that these problems will occur. Theoptimum situation would be printer components whose inherent function isable to preclude these problem issues from arising. In reality, the manydifferent types of operating conditions, and mishaps or unduly roughhandling during transport or day to day operation, make it impossible toaddress the above problems via the ‘passive’ control of componentdesign, material selection and so on.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides an inkjetprinter comprising:

an ink supply;

a printhead integrated circuit (IC) in fluid communication with the inksupply via an upstream ink line, the printhead IC having an array ofnozzles each with respective actuators for ejecting drops of ink ontoprint media;

a waste ink outlet in fluid communication with the printhead IC via adownstream ink line;

an upstream shut off valve in the upstream ink line; and,

a downstream pump mechanism in the downstream ink line.

The invention gives the user active control of the ink flows from theink reservoir to the nozzles of the printhead IC with the addition of asimple pump and valve. In the event that problems such as ink flooding,color mixing or printhead depriming occur, the user can follow simpletroubleshooting protocols to rectify the situation.

Optionally, the pump mechanism is reversible for pumping ink toward thewaste ink outlet or toward the ink manifold. Preferably, the pumpmechanism is a peristaltic pump.

Optionally, the printer further comprises a pressure regulator upstreamof the printhead IC for maintaining ink in the nozzles at a hydrostaticpressure less than atmospheric pressure. Preferably, the ink supply isan ink tank upstream of the shut off valve, and the pressure regulatoris positioned in the ink tank. In a further preferred form, the pressureregulator is a bubble point regulator which has an air bubble outletsubmerged in the ink in the ink tank, and an air inlet vented toatmosphere such that any reduction of hydrostatic pressure in the in theink tank because of ink consumption draws air through the air inlet toform bubbles at the bubble outlet and keep the pressure in the ink tanksubstantially constant.

Optionally, the printer further comprises a filter upstream of theprinthead IC for removing particulates from the ink. Preferably, the inktank has an outlet in sealed fluid communication with the shut off valveand the filter is positioned in the ink tank, covering the outlet. In aparticularly preferred form, the ink tank is a removable ink cartridgeand the outlet can releasably engage the upstream ink line.

Optionally, the shut off valve is biased shut and returns to its shutposition when the printer is powered down (switched off or in power savestand-by mode). Preferably, the shut off valve displaces ink when movingto its shut position such that when the shut off valves opens, a finitevolume of ink is drawn away from the ink tank to drop the hydrostaticpressure at the bubble outlet toward the bubble point pressure.

Optionally, the printer further comprises a capper that is movablebetween an unsealed position spaced from the nozzles of the printhead ICand a sealed position creating an air tight seal over the nozzles.Preferably, the array of nozzles is formed in a nozzle plate and thecapper is configured to remove ink and particulates deposited on thenozzle plate.

Optionally, the printer further comprises a sensor downstream of theprinthead IC for sensing the presence or absence of ink. Preferably, thesensor is upstream of the peristaltic pump. In a particularly preferredform, the printer has a plurality of the ink tanks for separate inkcolors, and a plurality of upstream ink lines and downstream ink linesfor each colour respectively, wherein the peristaltic pump is amulti-channel peristaltic pump that can pump each ink colorsimultaneously. Preferred embodiments may further comprise a controlleroperatively linked to the sensor and the peristaltic pump such that thecontroller operates the pump in response to output from the sensor.Optionally, the waste ink outlet leads to a sump.

According to a second aspect, the present invention provides a printheadassembly for installation in an inkjet printer, the printhead assemblycomprising:

a printhead integrated circuit (IC) having an array of nozzles each withrespective actuators for ejecting drops of ink onto print media;

an upstream ink line in fluid communication with the printhead IC, theupstream ink line being configured for releasable engagement with an inksupply;

a downstream ink line in fluid communication with the printhead IC;

a waste ink outlet in fluid communication with the printhead IC via thedownstream ink line;

an upstream shut off valve in the upstream ink line; and,

a downstream pump mechanism in the downstream ink line.

Optionally, the pump mechanism is reversible for pumping ink toward thewaste ink outlet or toward the printhead IC. Preferably, the pumpmechanism is a peristaltic pump.

Optionally the ink supply is an ink cartridge and the upstream ink lineis configured for releasable sealed fluid engagement with an outlet onthe ink cartridge.

Optionally, the shut off valve is biased shut and returns to its shutposition when the printhead assembly is installed in the printer and theprinter is powered down (switched off or in power save stand-by mode).Preferably, the shut off valve displaces ink when moving to its shutposition such that when the shut off valves opens, a finite volume ofink is drawn away from the ink cartridge to drop the hydrostaticpressure at the outlet of the ink cartridge.

Optionally, the printhead assembly further comprises a capper that ismovable between an unsealed position spaced from the nozzles of theprinthead IC and a sealed position creating an air tight seal over thenozzles. Preferably, the array of nozzles is formed in a nozzle plateand the capper is configured to remove ink and particulates deposited onthe nozzle plate.

Optionally, the printhead assembly further comprises a sensor downstreamof the ink manifold for sensing the presence or absence of ink.Preferably, the sensor is upstream of the peristaltic pump. In aparticularly preferred form, the printer has a plurality of the inktanks for separate ink colors, and a plurality of upstream ink lines anddownstream ink lines for each colour respectively, wherein theperistaltic pump is a multi-channel peristaltic pump that can pump eachink color simultaneously. Preferred embodiments may further comprise acontroller operatively linked to the sensor and the peristaltic pumpsuch that the controller operates the pump in response to output fromthe sensor. Optionally, the waste ink outlet connects to a sump in theprinter.

According to a third aspect, the present invention provides a printheadassembly for an inkjet printer, the printhead assembly comprising:

a printhead integrated circuit (IC) with an array of nozzles forejecting ink onto print media; and,

a shut off valve having:

-   -   a valve body defining an ink inlet for connection to an ink        supply, an ink outlet connected to the printhead IC, and a valve        seat;    -   a valve member biased into sealing engagement with the valve        seat to provide a fluid seal between the ink inlet and the ink        outlet; and,    -   an actuator for unsealing the valve member from the valve seat        upon energizing and re-sealing the valve member to the valve        seat when de-energized.

The invention protects the ink in the ink supply from contaminants thatcan migrate up the ink line during shut down periods. The valve memberis constantly biased to a closed position and so seals the ink supplyfrom the printhead IC as a default condition even in the event of apower failure. The bias is strong enough to provide the fluid seal sothat the seal is not compromised when the pressure difference betweenthe inlet and the outlet is small.

Preferably, the valve member has a diaphragm, and the ink outlet and theink inlet are both in fluid communication with one side of thediaphragm, such that unsealing the valve member draws the diaphragm awayfrom the valve seat to lower the fluid pressure in the ink inlet and theink outlet. In a further preferred form, the diaphragm is under residualtension when biasing the valve member into sealing engagement with thevalve seat. Optionally, the actuator works against the bias of thediaphragm to unseal the valve member from the valve seat. Optionally,the actuator has a solenoid. Optionally, the actuator has a shape memoryalloy. Optionally, the shape memory alloy comprises a Nitinol™ wire.Optionally the diaphragm is polyurethane.

Preferably the actuator draws the diaphragm away from the valve seatmore quickly than the diaphragm reseals the valve member to the valveseat. In a further preferred form, the valve seat has a frusto-conicalsurface for sealing against a complementary surface extending from oneside of the diaphragm.

According to a fourth aspect, the present invention provides an inkjetprinter comprising:

an ink supply;

a printhead integrated circuit (IC) in fluid communication with the inksupply via an upstream ink line, the printhead IC having an array ofnozzles each with respective actuators for ejecting drops of ink ontoprint media;

a waste ink outlet in fluid communication with the printhead IC via adownstream ink line;

an upstream pump mechanism in the upstream ink line;

a downstream pump mechanism in the downstream ink line; and,

user controls to selectively activate the upstream pump mechanism andthe down stream pump mechanism.

Giving the printer user the ability to selectively pump ink through thefluidic architecture both upstream and down stream of the printhead IC,allows many of the problems associated with MEMS printheads to becorrected after they occur. In light of this, it is not as crucial thatthe printer components themselves safeguard against issues such asde-prime, color mixing and outgassing. An active control system for theink flow through the printer means that the user can prime, deprime, orpurge the printhead IC. Also, the upstream line can be deprimed and/orthe downstream line can be deprimed (and of course subsequentlyre-primed). This control system allows the user to correct and printartifact causing conditions as and when they occur.

Preferably, the upstream ink line has an upstream bypass line around theupstream pump mechanism, the upstream bypass line having an upstreamshutoff valve.

Preferably, the downstream ink line has a downstream bypass line aroundthe downstream pump mechanism, the downstream bypass line having adownstream shutoff valve.

Preferably, the waste ink outlet feeds a sump for storing waste ink inthe printer.

Preferably, the user controls can selectively open and shut the upstreamand downstream shutoff valves.

Preferably, the upstream and downstream pump mechanisms are reversibleso that they can pump ink in either direction in the upstream anddownstream ink lines respectively.

Preferably, the upstream ink line terminates at an LCP moulding to whichthe printhead IC is mounted, and the downstream ink line starts at theLCP moulding.

Preferably, the upstream pump mechanism and the downstream pumpmechanism are provided by separate fluid lines running through a singlefluid pump.

Preferably the fluid pump is a peristaltic pump.

Preferably the upstream ink line and the downstream ink line have anadditional shutoff valve upstream of the fluid pump.

Alternatively, the upstream bypass valve and the downstream bypass valveare each substituted for a 3-way valve at the 3-way junctions upstreamof the fluid pump in both the upstream and downstream ink lines.

According to a fifth aspect, the present invention provides an inkdistribution member for providing ink from an ink supply to a printheadIC and a waste ink outlet, the distribution member comprising:

a series of ink conduits, each ink conduit having an aperture for fluidcommunication with associated nozzles in the printhead IC, an upstreamsection extending from the aperture towards the ink supply and adownstream section extending from the aperture to the waste ink outlet;wherein,

each of the ink conduits is geometrically profiled such that any gasbubbles extending across one if the ink conduits is urged from theupstream section towards the downstream section.

Outgassing from the ink into the small conduits of the LCP moulding cancreate readily visible artifacts in the print. Using an ink distributionmember that has profiled conduits that use capillarity or other means todraw bubble into the downstream ink line, will help to minimize bubblecontamination of the printhead IC. It can also be used to promote thepreferential filling of conduits containing larger ink bubbles overthose with smaller ink bubbles so that priming occurs more uniformly.

Preferably, the ink conduits are geometrically profiled so that theytaper in at least one cross sectional dimension from the downstreamsection to the start of the upstream section.

Preferably, the ink conduits are geometrically profiled so thatcapillarity effects urge the gas bubbles from the upstream section tothe downstream section.

Preferably, the upstream section is shorter than the downstream section.

Preferably, the ink conduit is profiled such that gas bubble are drawnpassed the aperture and into the downstream section.

Preferably ink distribution member is an LCP moulding.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described by way ofexample only with reference to the accompanying drawings, in which:

FIG. 1 shows a top perspective view of a prior art printhead assembly;

FIG. 2 shows an exploded view of the printhead assembly shown in FIG. 1;

FIG. 3 shows an inverted exploded view of the printhead assembly shownin FIG. 1;

FIG. 4 shows a cross-sectional end view of the printhead assembly ofFIG. 1;

FIG. 5 shows a magnified partial perspective view of the drop triangleend of a printhead integrated circuit module as shown in FIGS. 2 to 4;

FIG. 6 shows a magnified perspective view of the join between twoprinthead integrated circuit modules shown in FIGS. 2 to 5;

FIG. 7 shows an underside view of the printhead integrated circuit shownin FIG. 5;

FIG. 8 shows a transparent top view of a printhead assembly of FIG. 15showing in particular, the ink conduits for supplying ink to theprinthead integrated circuits;

FIG. 9 is a partial enlargement of FIG. 8;

FIG. 10 is an enlarged view of gas bubbles in the conduits of the LCPmoulding;

FIG. 11 is a sketch of the artifacts that can result from bubblecontamination of the ink lines;

FIG. 12A is a sketch of the LCP moulding and the printhead IC in afluidic system of the prior art;

FIG. 12B is a sketch showing the ink line bifurcations in the prior artfluidic system;

FIG. 13A is a sketch of the LCP moulding and the printhead IC in afluidic system of the present invention;

FIG. 13B is a sketch showing the ink line bifurcations in the fluidicsystem of the present invention;

FIG. 14 is a schematic cross section of the LCP moulding and theprinthead IC in a fluidic system of the present invention;

FIGS. 15A to 15C show the LCP conduit profiling for passive bubblecontrol;

FIGS. 16 to 21 show the various unit operations that are possible withthe active control provided by the present invention;

FIG. 22 shows a single pump/four valve implementation of the fluidicsystem;

FIG. 23 shows a single pump/two valve implementation of the fluidicsystem;

FIG. 24 is a sketch of another single pump fluidic system;

FIGS. 25A and 25B schematically show the fluidic system FIG. 24 and theinitial priming of the printhead IC;

FIGS. 26A to 26E schematically show the operational stages of thefluidic system FIG. 24 moving from standby to print ready mode;

FIGS. 27A and 27B schematically show the fluidic system FIG. 24 movingto a long term power down mode/move printer mode;

FIGS. 28A and 28C schematically show the fluidic system FIG. 24recovering from long term power down/deprime/gross color mixing;

FIG. 29 is a perspective view of a shut off valve; and,

FIG. 30 is a partial section view of the shut off valve.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The printers using prior art types of fluid architecture are exemplifiedby the disclosure in the Assignee's co-pending U.S. Ser. No. 11/014,769(our docket RRC001US) which is incorporated herein by cross referenceFor context, the printhead assembly from this printer design will bedescribed before the embodiments of the present invention.

Printhead Assembly

The printhead assembly 22 shown in FIGS. 1 to 4 is adapted to beattached to the underside of the main body 20 to receive ink from theoutlets molding 27 (see FIG. 10 of U.S. Ser. No. 11/014,769, our docketRRC001US, cross referenced above).

The printhead assembly 22 generally comprises an elongate upper member62 which is configured to extend beneath the main body 20 between theposts 26. U-shaped clips 63 project from the upper member 62. These passthrough the recesses 37 provided in the rigid plate 34 and becomecaptured by lugs (not shown) formed in the main body 20 to secure theprinthead assembly 22.

The upper element 62 has a plurality of feed tubes 64 that are receivedwithin the outlets in the outlet molding 27 when the printhead assembly22 secures to the main body 20. The feed tubes 64 may be provided withan outer coating to guard against ink leakage.

The upper member 62 is made from a liquid crystal polymer (LCP) whichoffers a number of advantages. It can be molded so that its coefficientof thermal expansion (CTE) is similar to that of silicon. It will beappreciated that any significant difference in the CTE's of theprinthead integrated circuit 74 (discussed below) and the underlyingmoldings can cause the entire structure to bow. However, as the CTE ofLCP in the mold direction is much less than that in the non-molddirection (˜5 ppm/° C. compared to ˜20 ppm/° C.), care must be take toensure that the mold direction of the LCP moldings is unidirectionalwith the longitudinal extent of the printhead integrated circuit (IC)74. LCP also has a relatively high stiffness with a modulus that istypically 5 times that of ‘normal plastics’ such as polycarbonates,styrene, nylon, PET and polypropylene.

As best shown in FIG. 2, upper member 62 has an open channelconfiguration for receiving a lower member 65, which is bonded thereto,via an adhesive film 66. The lower member 65 is also made from an LCPand has a plurality of ink channels 67 formed along its length. Each ofthe ink channels 67 receive ink from one of the feed tubes 64, anddistribute the ink along the length of the printhead assembly 22. Thechannels are 1 mm wide and separated by 0.75 mm thick walls.

In the embodiment shown, the lower member 65 has five channels 67extending along its length. Each channel 67 receives ink from only oneof the five feed tubes 64, which in turn receives ink from one of theink storage modules 45 (see FIG. 10 of U.S. Ser. No. 11/014,769, ourdocket RRC001US, cross referenced above) to reduce the risk of mixingdifferent colored inks. In this regard, adhesive film 66 also acts toseal the individual ink channels 67 to prevent cross channel mixing ofthe ink when the lower member 65 is assembled to the upper member 62.

In the bottom of each channel 67 are a series of equi-spaced holes 69(best seen in FIG. 3) to give five rows of holes 69 in the bottomsurface of the lower member 65. The middle row of holes 69 extends alongthe centre-line of the lower member 65, directly above the printhead IC74. As best seen in FIG. 8, other rows of holes 69 on either side of themiddle row need conduits 70 from each hole 69 to the centre so that inkcan be fed to the printhead IC 74.

Referring to FIG. 4, the printhead IC 74 is mounted to the underside ofthe lower member 65 by a polymer sealing film 71. This film may be athermoplastic film such as a PET or Polysulphone film, or it may be inthe form of a thermoset film, such as those manufactured by ALtechnologies and Rogers Corporation. The polymer sealing film 71 is alaminate with adhesive layers on both sides of a central film, andlaminated onto the underside of the lower member 65. As shown in FIGS.3, 8 and 9, a plurality of holes 72 are laser drilled through theadhesive film 71 to coincide with the centrally disposed ink deliverypoints (the middle row of holes 69 and the ends of the conduits 70) forfluid communication between the printhead IC 74 and the channels 67.

The thickness of the polymer sealing film 71 is critical to theeffectiveness of the ink seal it provides. As best seen in FIGS. 7 and8, the polymer sealing film seals the etched channels 77 on the reverseside of the printhead IC 74, as well as the conduits 70 on the otherside of the film. However, as the film 71 seals across the open end ofthe conduits 70, it can also bulge or sag into the conduit. The sectionof film that sags into a conduit 70 runs across several of the etchedchannels 77 in the printhead IC 74. The sagging may cause a gap betweenthe walls separating each of the etched channels 77. Obviously, thisbreaches the seal and allows ink to leak out of the printhead IC 74 andor between etched channels 77.

To guard against this, the polymer sealing film 71 should be thickenough to account for any sagging into the conduits 70 while maintainingthe seal over the etched channels 77. The minimum thickness of thepolymer sealing film 71 will depend on:

1. the width of the conduit into which it sags;

2. the thickness of the adhesive layers in the film's laminatestructure;

3. the ‘stiffness’ of the adhesive layer as the printhead IC 74 is beingpushed into it; and,

4. the modulus of the central film material of the laminate.

A polymer sealing film 71 thickness of 25 microns is adequate for theprinthead assembly 22 shown. However, increasing the thickness to 50,100 or even 200 microns will correspondingly increase the reliability ofthe seal provided.

Ink delivery inlets 73 are formed in the ‘front’ surface of a printheadIC 74. The inlets 73 supply ink to respective nozzles (described inFIGS. 23 to 36 of U.S. Ser. No. 11/014,769, our docket RRC001US, crossreferenced above) positioned on the inlets. The ink must be delivered tothe IC's so as to supply ink to each and every individual inlet 73.Accordingly, the inlets 73 within an individual printhead IC 74 arephysically grouped to reduce ink supply complexity and wiringcomplexity. They are also grouped logically to minimize powerconsumption and allow a variety of printing speeds.

Each printhead IC 74 is configured to receive and print five differentcolours of ink (C, M, Y, K and IR) and contains 1280 ink inlets percolour, with these nozzles being divided into even and odd nozzles (640each). Even and odd nozzles for each colour are provided on differentrows on the printhead IC 74 and are aligned vertically to perform true1600 dpi printing, meaning that nozzles 801 are arranged in 10 rows, asclearly shown in FIG. 5. The horizontal distance between two adjacentnozzles 801 on a single row is 31.75 microns, whilst the verticaldistance between rows of nozzles is based on the firing order of thenozzles, but rows are typically separated by an exact number of dotlines, plus a fraction of a dot line corresponding to the distance thepaper will move between row firing times. Also, the spacing of even andodd rows of nozzles for a given colour must be such that they can sharean ink channel, as will be described below.

As alluded to previously, the present invention is related to page-widthprinting and as such the printhead ICs 74 are arranged to extendhorizontally across the width of the printhead assembly 22. To achievethis, individual printhead ICs 74 are linked together in abuttingarrangement across the surface of the adhesive layer 71, as shown inFIGS. 2 and 3. The printhead IC's 74 may be attached to the polymersealing film 71 by heating the IC's above the melting point of theadhesive layer and then pressing them into the sealing film 71, ormelting the adhesive layer under the IC with a laser before pressingthem into the film. Another option is to both heat the IC (not above theadhesive melting point) and the adhesive layer, before pressing it intothe film 71.

The length of an individual printhead IC 74 is around 20-22 mm. To printan A4/US letter sized page, 11-12 individual printhead ICs 74 arecontiguously linked together. The number of individual printhead ICs 74may be varied to accommodate sheets of other widths.

The printhead ICs 74 may be linked together in a variety of ways. Oneparticular manner for linking the ICs 74 is shown in FIG. 6. In thisarrangement, the ICs 74 are shaped at their ends to link together toform a horizontal line of ICs, with no vertical offset betweenneighboring ICs. A sloping join is provided between the ICs havingsubstantially a 45° angle. The joining edge is not straight and has asawtooth profile to facilitate positioning, and the ICs 74 are intendedto be spaced about 11 microns apart, measured perpendicular to thejoining edge. In this arrangement, the left most ink delivery nozzles 73on each row are dropped by 10 line pitches and arranged in a triangleconfiguration. This arrangement provides a degree of overlap of nozzlesat the join and maintains the pitch of the nozzles to ensure that thedrops of ink are delivered consistently along the printing zone. Thisarrangement also ensures that more silicon is provided at the edge ofthe IC 74 to ensure sufficient linkage. Whilst control of the operationof the nozzles is performed by the SoPEC device (discussed later in ofU.S. Ser. No. 11/014,769, our docket RRC001US, cross referenced above),compensation for the nozzles may be performed in the printhead, or mayalso be performed by the SoPEC device, depending on the storagerequirements. In this regard it will be appreciated that the droppedtriangle arrangement of nozzles disposed at one end of the IC 74provides the minimum on-printhead storage requirements. However wherestorage requirements are less critical, shapes other than a triangle canbe used, for example, the dropped rows may take the form of a trapezoid.

The upper surface of the printhead ICs have a number of bond pads 75provided along an edge thereof which provide a means for receiving dataand or power to control the operation of the nozzles 73 from the SoPECdevice. To aid in positioning the ICs 74 correctly on the surface of theadhesive layer 71 and aligning the ICs 74 such that they correctly alignwith the holes 72 formed in the adhesive layer 71, fiducials 76 are alsoprovided on the surface of the ICs 74. The fiducials 76 are in the formof markers that are readily identifiable by appropriate positioningequipment to indicate the true position of the IC 74 with respect to aneighboring IC and the surface of the adhesive layer 71, and arestrategically positioned at the edges of the ICs 74, and along thelength of the adhesive layer 71.

In order to receive the ink from the holes 72 formed in the polymersealing film 71 and to distribute the ink to the ink inlets 73, theunderside of each printhead IC 74 is configured as shown in FIG. 7. Anumber of etched channels 77 are provided, with each channel 77 in fluidcommunication with a pair of rows of inlets 73 dedicated to deliveringone particular colour or type of ink. The channels 77 are about 80microns wide, which is equivalent to the width of the holes 72 in thepolymer sealing film 71, and extend the length of the IC 74. Thechannels 77 are divided into sections by silicon walls 78. Each sectionis directly supplied with ink, to reduce the flow path to the inlets 73and the likelihood of ink starvation to the individual nozzles. In thisregard, each section feeds approximately 128 nozzles 801 via theirrespective inlets 73.

FIG. 9 shows more clearly how the ink is fed to the etched channels 77formed in the underside of the ICs 74 for supply to the nozzles 73. Asshown, holes 72 formed through the polymer sealing film 71 are alignedwith one of the channels 77 at the point where the silicon wall 78separates the channel 77 into sections. The holes 72 are about 80microns in width which is substantially the same width of the channels77 such that one hole 72 supplies ink to two sections of the channel 77.It will be appreciated that this halves the density of holes 72 requiredin the polymer sealing film 71.

Following attachment and alignment of each of the printhead ICs 74 tothe surface of the polymer sealing film 71, a flex PCB 79 (see FIG. 4)is attached along an edge of the ICs 74 so that control signals andpower can be supplied to the bond pads 75 to control and operate thenozzles. As shown more clearly in FIG. 1, the flex PCB 79 extends fromthe printhead assembly 22 and folds around the printhead assembly 22.

The flex PCB 79 may also have a plurality of decoupling capacitors 81arranged along its length for controlling the power and data signalsreceived. As best shown in FIG. 2, the flex PCB 79 has a plurality ofelectrical contacts 180 formed along its length for receiving power andor data signals from the control circuitry of the cradle unit 12. Aplurality of holes 80 are also formed along the distal edge of the flexPCB 79 which provide a means for attaching the flex PCB to the flangeportion 40 of the rigid plate 34 of the main body 20. The manner inwhich the electrical contacts of the flex PCB 79 contact the power anddata contacts of the cradle unit 12 will be described later.

As shown in FIG. 4, a media shield 82 protects the printhead ICs 74 fromdamage which may occur due to contact with the passing media. The mediashield 82 is attached to the upper member 62 upstream of the printheadICs 74 via an appropriate clip-lock arrangement or via an adhesive. Whenattached in this manner, the printhead ICs 74 sit below the surface ofthe media shield 82, out of the path of the passing media.

A space 83 is provided between the media shield 82 and the upper 62 andlower 65 members which can receive pressurized air from an aircompressor or the like. As this space 83 extends along the length of theprinthead assembly 22, compressed air can be supplied to the space 56from either end of the printhead assembly 22 and be evenly distributedalong the assembly. The inner surface of the media shield 82 is providedwith a series of fins 84 which define a plurality of air outlets evenlydistributed along the length of the media shield 82 through which thecompressed air travels and is directed across the printhead ICs 74 inthe direction of the media delivery. This arrangement acts to preventdust and other particulate matter carried with the media from settlingon the surface of the printhead ICs, which could cause blockage anddamage to the nozzles.

Active Ink Flow Control System

The present invention gives the user a versatile control system forcorrecting many of the detrimental conditions that are possible duringthe operative life of the printer. It is also capable of preparing theprinthead for transport, long term storage and re-activation. It canalso allow the user to establish a desired negative pressure at theprinthead IC nozzles. The control system requires easily incorporatedmodifications to the prior art printer designs described above.

Printhead Maintenance Requirements

The printer's maintenance system should meet several requirements:

sealing for hydration

sealing to exclude particulates

drop ejection for hydration

drop ejection for ink purge

correction of dried nozzles

correction of flooding

correction of particulate fouling

correction of outgassing

correction of color mixing and

correction of deprime

Various mechanisms components within the printer assembly are designedwith a view to minimizing any problems that the printhead maintenancesystem will need to address. However, it is unrealistic to expect thatthe design of the printer assembly components can deal with all theproblems that arise for the printhead maintenance system. In relation tosealing the nozzle face for hydration and sealing the nozzles to excludeparticulates the maintenance system can incorporate a capping memberwith a perimeter seal that will achieve these two requirements.

Drop ejection for hydration (or keep wet drops) and drop ejection forink purge require the print engine controller (PEC) to play a roll inthe overall printhead maintenance system.

The particulate fouling can be dealt with using filters positionedupstream of the printhead. However, care must be taken that small sizedfilters do not become too much of a flow constriction. By increasing thesurface area of the filter the appropriate ink supply rate to theprinthead can be maintained.

Correcting a flooded printhead will typically involve some type ofblotting or wiping mechanism to remove beads of ink on the nozzle faceof the printhead. Methods and systems for removing ink flooded across anink ejection face of a printhead are described in our earlier filed U.S.application Ser. No. 11/246,707 (“Printhead Maintenance Assembly withFilm Transport of Ink”), Ser. No. 11/246,706 (“Method of Maintaining aPrinthead using Film Transport of Ink”), Ser. No. 11/246,705 (“Method ofRemoving Ink from a Printhead using Film Transfer”), and Ser. No.11/246,708 (“Method of Removing Particulates from a Printhead using FilmTransfer”), all filed on Oct. 11, 2005. The contents of each of these USapplications are incorporated herein by reference.

Dried nozzles, outgassing, color mixing and nozzle deprime are moredifficult to correct as they typically require a strong ink purge.Purging ink is relatively wasteful and creates an ink removal problemfor the capping mechanism. Again the arrangements described in the abovereferenced US applications incorporate an ink collection and transportto sump function.

Outgassing is a significant problem for printheads having micron scalefluid flow conduits. Outgassing occurs when gasses dissolved in the ink(typically nitrogen) come out of solution to form bubbles. These bubblescan lodge in the ink line or even the ink ejection chambers and preventthe downstream nozzles from ejecting.

FIG. 10 shows the underside of the LCP moulding 65. Conduits 69 extendbetween the point where the printed IC (not shown) is mounted and theholes 69. Bubbles from outgassing 100 form in the upstream ink line andfeed down to the printed IC.

FIG. 11 shows the artifacts that result from outgassing bubbles. As thebubbles 100 feed into the printhead IC, the nozzles deprime and startejecting the bubble gas rather than ink. This appears as arrow headshaped artifacts 102 in the resulting print. Hopefully pressure fromupstream ink flow eventually clears the bubble from the printhead IC andthe artifacts disappear. However, the bubbles 100 can have a tendency toget stuck at conduit discontinuities. Discontinuities such as thesilicon wall 78 across the channel 77 in the printhead IC (see FIG. 9)tend to trap some of the bubbles and effectively form an ink blockage tonozzles fed from that end of the channel 77. These usually result instreak type artifacts 104 extending from the bottom corners of the arrowhead artifact 102. There is a significant risk that these bubbles do noteventually clear with continued printing which can result in persistentartifacts or nozzle burn out from lack of ink cooling.

Another problem that is difficult to address using component design iscolor mixing. Color mixing occurs when ink of one color establishes afluid connection with ink of another color via the face of the nozzleplate. Ink from one ink loan can be driven into the ink loan of adifferent color by slightly different hydraulic pressures within eachline, osmotic pressure differences and even simple diffusion.

Capping and wiping the nozzle plate will remove the vast majority ofparticulates that create the fluid flow path between nozzles. However,printhead IC's with high nozzle densities require only a single piece ofpaper dust or thin surface film to create significant color mixing whilethe printer is left idle for hours or overnight.

Instead of placing a heavy reliance on the design of the printheadassembly components to deal with factors that give rise to printheadmaintenance issues, the present invention uses an active control systemfor the printhead maintenance regime to correct issues as they arise.

FIGS. 12A and 12B are a schematic representation of the fluidarchitecture for the printhead shown in FIGS. 1 to 11. The different inkcolors are fed to the channels 67 in an LCP moulding and fed throughholes 69 to the smaller conduits 70 that lead to the printhead IC 74. Asbest seen in FIG. 12D, this architecture terminates the ink line at theprinthead IC 74. Hence any attempts to change the ink flow conditionswithin the printhead IC 74 need to occur by intervention upstream.

FIGS. 13A and 13B sketch a fluid ink architecture in which the printheadIC 74 is not the end of the ink line. The small conduits 70 in the LCPmoulding do not terminate at the holes feeding the printhead IC 74 butrather continue on to downstream channels 108 feeding holes 110 intodownstream channels 106 in the LCP moulding. In this way bubbles in theink line do not need to be purged out through the printhead IC 74.Instead the bubbles can completely bypass the printhead IC 74 in favorof the downstream ink conduits 108.

As shown in FIG. 13B the ink line upstream of the printhead IC 74 has apump 114 as does the downstream ink line 116. This provides the controlsystem with even greater flexibility for creating desired flowconditions within the ink line in general and the printhead IC 74 inparticular.

The downstream pump 116 feeds to sump 118 and this highlights that thefluid architecture of the present system creates more waste ink than thearchitecture sketched in FIGS. 12A and 12B.

FIG. 14 is a schematic section view through the LCP moulding, thepolymer sealing film 21 and the printhead IC 74. It illustrates the inkflow from the LCP channel 67 to the upstream conduit 70 past the inlet72 (see FIG. 9) to the printhead IC 74 to the downstream ink conduit 108but feeds the downstream LCP channel 106. It will be appreciated thatthe upstream conduit 17 and the downstream conduit 108 are essentially asingle conduit 120.

FIGS. 15A, 15B and 15C illustrate how the walls of the conduits 120 canbe profiled to better control the position of any bubbles thatinevitably contaminate the ink line. FIG. 15A shows two conduits 120feeding ink between the upstream LCP channel 67 and the downstream LCPchannel 106 both conduits have bubbles contaminating the ink flow.However, bubble 126 in the left hand conduit 120 is significantlysmaller than the bubble 124 in the right hand conduit. By tapering theupstream conduit 70 from the printhead IC towards the upstream LCPchannel 67 the bubble 124 is forced to have part of its surface with ahigher radius of curvature 122. The smaller bubble 126 has a relativelylarge radius of curvature 128. The higher degree of curvature at 122creates a stronger capillary force for drawing ink down the upstream end70 of the right hand ink conduit 120.

As shown in FIG. 15B profiling the sides of the ink conduits 120 tend tomake the bubble contaminants 126 and 124 become a uniform size such thatthe printhead IC 74 is primed and deprimed more uniformly.

As shown in FIG. 15C profiling the ink conduit 120 can be used to moveink bubbles 100 past the printhead IC 74 to minimise the amount ofbubble contamination within the ejection nozzles and chambers. Bytapering the sides of the ink conduit 120 from the downstream LCPchannel 106 to the upstream LCP channel 67, the bubble 100 will tend tohave a smaller radius of curvature 122 at its downstream end than itsupstream end 128. Because of the surface tension and capillarity thebubble 100 is biased towards the downstream LCP channel 106 and so tendsnot to become lodged at the inlets to the printhead IC 74. The printheadIC 74 may draw in small amounts of the air bubble 100 but it is notforced to expel the entire bubble as with the architecture shown inFIGS. 12A and 12B.

The versatility of the control system will now be illustrated withreference to FIGS. 16 to 21. As shown in FIG. 16, both of the upstreamand downstream pumps 114 and 116 have a shutoff valve in a parallelbypass line (113 and 132 respectively). To prime the fluidic system withink up to the back of the printhead IC 74 the controller sets bothshutoff valves 113 and 132 to “close”. The upstream pump 114 pushes inkthrough the upstream LCP channel 67 and down the upstream end of theconduits 120. The downstream pump 116 is driven at a slightly higherrate. Typically it operates at about 20% more capacity than the upstreampump 114. As the upstream pump has a lower capacity than the downstreampump the difference in the flow rate is made up by air drawn in throughthe printhead IC 74. This ensures that the fluidic architecture isprimed with ink up to the back of the printhead IC 74 and all bubblecontaminants removed from the upstream LCP channel 67 and upstreamconduits 70.

FIG. 17 shows the system configuration for depriming the architecturedownstream with the printhead IC 74. Both the shut off valves 113 and132 are closed while the upstream pump is deactivated. When either pumpis deactivated, it essentially acts as a closed shutoff valve. Thismeans that the upstream end of the ink line is choked of any ink supply.Meanwhile the downstream pump 116 slowly draws any ink out of thedownstream ends 108 of the conduits 120 and the downstream LCP channel106. Eventually the downstream pump 116 is simply drawing air throughthe printhead IC 74. This configuration ensures that the system has bedeprimed downstream of the printhead IC 74.

FIG. 18 shows the system configuration for depriming the fluidarchitecture upstream of the printhead IC 74. With this configurationthe upstream shut off valve 130 is closed and the upstream pump isoperating in reverse. Meanwhile the downstream shut off valve 132 isopen and the downstream pump 116 is deactivated. The upstream pump 114draws any ink through the upstream lines 70 and 67 back towards thecartridge (not shown). The open shut off valve 132 will allow some ofthe ink in the downstream end of the ink lines 106 and 108. However,eventually the upstream pump 114 draws air only through the upstreamconduits 70 and 67 from the printhead IC 74.

FIG. 19 shows the system configuration for creating a desired negativepressure that the printhead IC 74. The advantages of having a negativehydrostatic pressure at the nozzles of the printhead IC are discussed indetails in the above referenced U.S. Ser. No. 11/014,769 (Docket No.RRC001US) filed Dec. 20, 2004. Both the upstream and downstream shut offvalves 113 and 132 are open. However, the upstream pump 114 isdeactivated and acts as a closed shut off valve. Downstream of theprinthead IC 74 the downstream pump 116 is activated but operatesrelatively slowly. As the shut off valve 132 is open the downstreamvalve 116 creates a flow circulating from the pump through thedownstream shut off valve 132 and the returning back through the pump116. As the upstream shut off valve 130 is open a small amount of inkfrom the downstream conduits 108 and 106 are drawn into the circulatingloop of ink by Venturi effects. For conservation of flow, a small amountof ink bleeds off to the sump.

As the Venturi effect from the circulating ink drops the hydrostaticpressure in the downstream conduits 108 and 106 the hydrostatic pressureat the printhead IC 74 also drops.

Referring to FIG. 20 the configuration for ink flow through or “purge”is shown. The upstream shut off valve 130 is closed however the upstreampump 114 is activated and supplying the upstream conduit 67 and 70 withink. The downstream shut off valve 132 is open while the downstream pump116 is deactivated and therefore closing that branch of the fluidsystem. This configuration draws ink directly from the supply and feedsit to the sump. This involves some degree of ink wastage however itpurges the entire architecture of bubbles caused by outgassing.

FIG. 21 shows the configuration needed to purge the printhead IC 74. Inthis configuration the downstream pump 116 and downstream shut off valve132 are deactivated and closed. This essentially creates a flowobstruction downstream of the printhead IC 74. Upstream of the printheadIC the upstream pump 114 is activated but the upstream shut off valve130 is closed. This forces ink out of the nozzles in the printhead ICuntil it beads and collects on the surface of the nozzle face. Fromthere, the purged ink can be collected and transported to the sump usinga mechanism such as those described in the above referenced co-pendingapplications filed in the US (U.S. Ser. No. 11/246,707, our docket no.FNE001US) on Oct. 11, 2005.

The active control system in by the present fluidic architecture offersa versatile range of operations that allow the user to recover theprinthead whenever artifacts are noticed. It also allows themanufacturer to ship the printhead IC's deprimed so that the user primesthem on initial start up. For example after final print testing of theprinthead assemblies are shipped dry. The control system is used todeprime upstream and then deprime downstream of the printhead IC 74.

During start up, the configuration shown in FIG. 16 is used to primeupstream then the configuration of FIG. 20 creates a flow throughcondition after which the configuration of FIG. 19 establishes anegative pressure at the printhead IC. During printing the configurationof FIG. 19 can maintain a desired negative pressure condition at theprinthead nozzles.

To correct dry nozzles or osmotic color mixing the user can deprimedownstream then prime upstream followed by establishing a negativepressure.

In order to address outgassing in the ink line, the user can perform aflow through purge as illustrated in FIG. 20.

In order to remove some external contamination of the printhead IC orink contamination within the ink lines, the control system can flood theprinthead as shown in FIG. 21 before re-establishing a negative pressureas shown in FIG. 19.

At the end of the print job, the control system can be set toautomatically deprime downstream of the printhead IC before the capperplaces a perimeter seal around the printhead IC.

The upstream and downstream pumps 114 and 116 can be provided byperistaltic pumps. In the printers of the type shown in the abovereferenced U.S. Ser. No. 11/014,769 (our docket RRC001US) theperistaltic pumps have a displacement resolution of 10 microliters. Thisequates to about 5 mm of travel on an appropriately dimensionalperistaltic tube. These specifications give the most flow rate of about3 millilitres per minute and very low pulse in the resulting flow.

The valves should preferably be zero displacement, zero leak, fast andeasy to actuate. Ordinary workers in this field will readily identify arange of valve mechanisms that satisfy these requirements.

Single Pump Implementations

FIG. 22 shows a first single pump implementation of the fluidic controlsystem. This implementation uses four shut off valves 134, 135, 136 and137 in order to direct ink flows past the printhead IC 74 and eventuallyto the sump 118. Set out in Table 1 below are the operational statusesfor each of the valves and the pump in order to provide the variouscontrol states within the architecture. In relation to the pump statuscolumn “down” is an indication that the peristaltic pump 114 is drivingink flow downwards as shown in FIG. 22 and “up” indicates ink flowupwards as it appears in FIG. 22.

TABLE 1 Single Pump/Four Valve Implementation Flow Valve Condition Pump114 134 Valve 135 Valve 136 Valve 137 prime down open Closed closed openprint up open Open closed closed flush down open Closed closed openflood down open Closed closed closed deprime down closed Closed openclosed downstream deprime up open Closed closed closed upstream standbydeactivated closed Closed closed Closed

FIG. 23 shows a second single pump implementation that uses only twovalves to achieve all the control states possible in the above describedimplementations. However in this implementation, the valves 138 and 140are 3-way valves and therefore slightly more expensive components.

Table 2 below sets out the operational status for each of the systemcomponents in order to achieve the flow conditions achieved by the twopump implementation.

TABLE 2 Single Pump to Valve Implementation Function Pump 114 Valve 138Valve 140 Prime Down Inline Inline Print Up Inline Recirculate FlushDown Inline Bypass Flood Down Inline Recirculate Deprime DownRecirculate Inline Downstream Deprime upstream Up Inline RecirculateStandby Up Recirculate Recirculate

FIG. 24 shows a third single pump implementation that further simplifiesthe fluidic architecture. It will be appreciated that only a single inkline is shown and a color printer would have separate lines (and ofcourse separate ink tanks 112) for each ink color. As shown in FIG. 24,this architecture has a single pump 114 downstream of the LCP moulding164, and a shut off valve 138 upstream of the LCP moulding. The LCPmoulding supports the printhead IC's 74 via the adhesive polymer film 71(see FIG. 2). The shut off valve 138 isolates the ink in the ink tank112 from the printhead IC's 74 whenever the printer is powered down.This prevents any color mixing at the printhead IC's 74 from reachingthe ink tank 112 during periods of inactivity. These issues arediscussed in more detail below with reference to the shut off valveshown in FIGS. 29 and 30.

The ink tank 112 has a venting bubble point pressure regulator 200 formaintaining a relatively constant negative hydrostatic pressure in theink at the nozzles. Bubble point pressure regulators within inkreservoirs are comprehensively described in co-pending application Ser.No. 11/640,355 (Our Docket RMC007US) filed 18 Dec. 2006 incorporatedherein by reference. However, for the purposes of this description theregulator 202 is shown as a bubble outlet 204 submerged in the ink ofthe tank 112 and vented to atmosphere via sealed conduit 204 extendingto an air inlet 206. As the printhead IC's 74 consume ink, the pressurein the tank 112 drops until the pressure difference at the bubble outlet202 sucks air into the tank. This air forms a forms a bubble in the inkwhich rises to the tank's headspace. This pressure difference is thebubble point pressure and will depend on the diameter (or smallestdimension) of the bubble outlet 202 and the Laplace pressure of the inkmeniscus at the outlet which is resisting the ingress of the air.

The bubble point regulator uses the bubble point pressure needed togenerate a bubble at the submerged bubble outlet 202 to keep thehydrostatic pressure at the outlet substantially constant (there areslight fluctuations when the bulging meniscus of air forms a bubble andrises to the headspace in the ink tank). If the hydrostatic pressure atthe outlet is at the bubble point, then the hydrostatic pressure profilein the ink tank is also known regardless of how much ink has beenconsumed from the tank. The pressure at the surface of the ink in thetank will decrease towards the bubble point pressure as the ink leveldrops to the outlet. Of course, once the outlet 202 is exposed, the headspace vents to atmosphere and negative pressure is lost. The ink tankshould be refilled, or replaced (if it is a cartridge) before the inklevel reaches the bubble outlet 202.

The ink tank 112 can be a fixed reservoir that can be refilled, areplaceable cartridge or (as disclosed in U.S. Ser. No. 11/014,769 ourdocket no. RRC001US incorporated by reference) a refillable cartridge.To guard against particulate fouling, the outlet 162 of the ink tank 112has a filter 160. As the system also contemplates limited reverse flow,some printers may incorporate a filter downstream of the printhead IC 74as well. However, as filters have a finite life, replacing old filtersby simply replacing the ink cartridge is particularly convenient for theuser. If the upstream and or downstream filters are a separateconsumable item, regular replacement relies on the user's diligence.

When the bubble outlet 202 is at the bubble point pressure, and the shutoff valve 138 is open, the hydrostatic pressure at the nozzles is alsoconstant and less than atmospheric. However, if the shut off valve 138has been closed for a period of time, outgassing bubbles may form in theLCP moulding 164 or the printhead IC's 74 that change the pressure atthe nozzles. Likewise, expansion and contraction of the bubbles fromdiurnal temperature variations can change the pressure in the ink line67 downstream of the shut off valve 138. Similarly, the pressure in theink tank can vary during periods of inactivity because of dissolvedgases coming out of solution.

The downstream ink line 106 leading from the LCP 164 to the pump 114 caninclude an ink sensor 152 linked to an electronic controller 154 for thepump. The sensor 152 senses the presence or absence of ink in thedownstream ink line 106. Alternatively, the system can dispense with thesensor 152, and the pump 114 can be configured so that it runs for anappropriate period of time for each of the various operations. This mayadversely affect the operating costs because of increased ink wastage.

The pump 114 feeds into a sump 184 (when pumping in the forwarddirection). The sump 184 is physically positioned in the printer so thatit is less elevated than the printhead ICs 74. This allows the column ofink in the downstream ink line 106 to ‘hang’ from the LCP 164 duringstandby periods, thereby creating a negative hydrostatic pressure at theprinthead ICs 74. A negative pressure at the nozzles draws the inkmeniscus inwards and inhibits color mixing. Of course, the peristalticpump 114 needs to be stopped in an open condition so that there is fluidcommunication between the LCP 164 and the ink outlet in the sump 184.

As discussed above, pressure differences between the ink lines ofdifferent colors can occur during periods of inactivity. Furthermore,paper dust or other particulates on the nozzle plate can wick ink fromone nozzle to another. Driven by the slight pressure differences betweeneach ink line, color mixing can occur while the printer is inactive. Theshut off valve 138 isolates the ink tank 112 from the nozzle of theprinthead IC's 74 to prevent color mixing extending up to the ink tank112. Once the ink in the tank has been contaminated with a differentcolor, it is irretrievable and has to be replaced. This is discussedfurther below in relation to the shut off valve's ability to maintainthe integrity of its seal when the pressure difference between theupstream and downstream sides of the valve is very small.

The capper 150 is a printhead maintenance station that seals the nozzlesduring standby periods to avoid dehydration of the printhead ICs 74 aswell as shield the nozzle plate from paper dust and other particulates.The capper 150 is also configured to wipe the nozzle plate to removedried ink and other contaminants. Dehydration of the printhead ICs 74occurs when the ink solvent, typically water, evaporates and increasesthe viscosity of the ink. If the ink viscosity is too high, the inkejection actuators fail to eject ink drops. Should the capper seal becompromised, dehydrated nozzles can be a problem when reactivating theprinter after a power down or standby period.

The problems outlined above are not uncommon during the operative lifeof a printer and can be effectively corrected with the relatively simplefluidic architecture shown in FIG. 24. It also allows the user toinitially prime the printer, deprime the printer prior to moving it, orrestore the printer to a known print ready state using simpletrouble-shooting protocols. Several examples of these situations are setout below.

Initial Priming

The printheads (or fully assembled printers) are shipped deprimed ofink. Priming a new dry printhead upon installation is shown in FIGS. 25Aand 25B. The capper 150 is applied to the printhead ICs 74 and the shutoff valve 138 is initially closed. As shown in FIG. 25A, there is no inkin the upstream LCP channels 70 or the downstream LCP channels 108. Anink sensor 156 at the peristaltic pump 114 registers the absence of inkto the controller 154.

Referring to FIG. 25B, the shut off valve 138 is opened and the pump 114pumps forward (from ink tank 112 to sump 184). Ink is infused into theupstream and downstream channels 70 and 108 of the LCP moulding. Inkfeeds into the printhead ICs 74 by capillary action. The multi-channelpump 114 (one channel per color) stops when the sensor 156 for all theink lines register the presence of ink. The nozzles may be fired intothe capper 150 to drop the pressure at the bubble outlet 202 to thebubble point pressure. On the other hand, simply printing the print jobsoon draws the pressure in the ink tank 112 down to the normal operatingpressure.

Color Mixing

If the nozzle plate remains clean, there is no capillary bridgingbetween the different ink lines. In most cases the capper 150 willeffectively clean the nozzle plate, but in the event that paper dustwicks ink between nozzles, the shut off valve 138 protects the ink tank112 from contamination. Mixing downstream of the shut off valve 138 canbe easily rectified during the ‘Standby-to-Ready’ procedure describedbelow.

Other techniques for guarding against color mixing include dehydratingthe nozzles, leaving the pump 114 in an open condition and sparse keepwet dots. Keep wet dots are normally used to stop nozzles from dryingout if the period between successive firings of a nozzle exceeds thedecap time. Decap occurs when evaporation from the nozzle increases inkviscosity to the point that it can not longer eject. However, sparse andinfrequent keep wet dots fired during standby will purge the nozzles ofany contaminated ink before it can migrate too far along the upstreamline.

Deliberately dehydrating the printhead ICs 74 prior to standby increasesthe ink viscosity and so inhibits its ability to wick across the nozzleplate. Simply warming the ink will dehydrate it and this can be achievedwith sub-ejection pulses to the printhead ICs 74.

As discussed above, leaving the peristaltic pump 114 in the openposition keeps the nozzles is in fluid communication with the waste inkoutlet at the sump 184. The weight of ink in the downstream ink line 106generates a negative pressure at the nozzles. A negative pressure at thenozzles creates a concave meniscus that is less prone to wick out ontothe nozzle plate.

Standby to Ready

FIG. 26A shows the printer in standby. The shut off valve 138 is closedand the pump 114 is open. The capper 150 is sealed over the printheadICs 74. If the printer has been in standby for a relatively short time(say, overnight), the ink will have dehydrated to a degree, but probablynot to the point where the nozzles have dried out. However, even milddehydration can visibly concentrate the ink and there may also be somecolor mixing. FIG. 26B shows the system configuration for purging theink upstream of the printhead ICs. The shut off valve 138 is opened andthe pump 114 is moved to a closed position (no fluid communicationbetween the printhead ICs 74 and the sump 184). Then the printhead ICs74 need to print a burst of dots with the capper 150 remaining in placeto blot the purged ink. The volume of ink to be purged will depend onthe printer, but as an indication the printhead shown in FIGS. 1 and 2needs to print the equivalent of about 10% to 30% of a page in processblack.

If the printer has been in standby for a longer period, the printheadmay be primed by dehydrated through to the LCP moulding supporting theprinthead ICs 74. In this case, the printhead ICs need to be primed withejectable ink. FIG. 26C shows the process for achieving this. With theshut off valve 138 closed, the pump 114 is driven in reverse a smallamount to force an ink flood 158 onto the nozzle plate of each IC 74. Asshown in FIG. 26D, the capper 150 wipes the printhead ICs 74 todistribute the flood 158 across the nozzle plate, while firing thenozzles to prevent any ink migrating back into the LCP moulding. If thisis not immediately successful, the process can be repeated until all thenozzles rehydrate.

When the printhead ICs 74 have rehydrated, the shut off valve 138 isopened (see FIG. 26E) and the pump 114 drives forward again and stops atthe open position. The nozzles in the printhead ICs 74 are fired onelast time to ensure there is no color mixing from wiping the ink floodacross the nozzle plate.

Power Down/Move Printer

FIGS. 27A and 27B show the procedure for a controlled power down (i.e.the user switching off the main power switch). This would be used whenthe user is moving the printer, placing it in storage or similar. Toavoid color mixing and flooding (because of jarring while being shifted)the printhead ICs 74 are deprimed. As shown in FIG. 27A, the shut offvalve 138 is closed, while the capper 150 unseals the printhead ICs 74and the pump 114 pumps forward to the sump.

Referring to FIG. 27B, air drawn through the nozzles deprimes theprinthead ICs 74 and the downstream ink line to the pump 114. When thesensor 156 registers a lack of ink, the pump 114 stops at the closedposition and the capper 150 seals the printhead ICs.

Power Failure

In the event of sudden failure of the power supply, the shut off valve138 is biased to close. This prevents any color mixing in the ink tank.The pump 114 may be open or closed and the capper 150 may be sealed orunsealed depending on the printer status at the time of power failure.However, as long as the shut off valve closes to protect the ink tank,all other conditions can be rectified by the user when the power isrestored.

Power Up

FIGS. 28A to 28C show the process for switching the printer on after apower down period. As the extent of deprime or color mixing is notknown, the worst case is assumed—thoroughly mixed ink downstream of theshut off valve 138 to the pump 114. Referring to FIG. 28A this is fixedby depriming the printhead ICs 74 and the downstream line to the pump114. The shut off valve 138 remains closed while the capper 150 unsealsthe nozzles and the pump 114 pumps the ink forward to the sump. When thesensor 156 reads a lack of ink, the capper 150 reseals the printhead ICs74 and the shut off valve 138 opens as shown in FIG. 28B. As shown inFIG. 28C, the ink upstream of the printhead ICs 74 is flushed through tothe pump 114. When the sensor 156 registers the presence of ink, theshut off valve closed, and the pump 114 can be stopped, preferably inthe open condition so that the hydrostatic pressure at the nozzles isless than atmospheric. The printer is now in Standby and to print, itsimply initiates the Standby to Ready procedure discussed above.

Deprime Recovery

In the unlikely event that one of the printhead ICs deprimes duringoperation, the user can quickly address the problem by sealing thenozzles with the capper, opening the shut off valve 138 and pumpingforward (as shown in FIG. 28 B). The LCP moulding refills with ink whichinfuses to the printhead ICs.

Flood Recovery

Should the printer get bumped or jarred, there is potential for theprinthead ICs to flood ink onto the nozzle plate. The user corrects thisby initiating the process set out if FIGS. 26C to 26E described above.

Gross Color Mixing

If the printed image reveals gross color mixing (cross contamination ofthe colors downstream of the shut off valve) the user should immediatelyfollow the Power Up procedure shown in FIGS. 28A to 28C. The printheadIC deprime and subsequent reprime recovers the printer from most failurestates (albeit not in the most ink economical way) and so may be themost frequently used remedy by the user.

Shut Off Valve

As discussed above, it is imperative that the ink tank is protected fromcolor mixing. Once the ink in the supply tank is contaminated, it isirretrievable and must be replaced. To achieve this, the shut off valve138 (see FIG. 24) should only be open when feeding ink to the printheadICs 74 or flushing color mixed ink from the LCP moulding 164. At othertimes, the ink tank 112 should be kept fluidically isolated.

In light of this, the shut off valve 138 needs to be biased closed. Anypower down should stop any fluid communication between the ink tank andthe printhead ICs 74. It is important that the fluid seal in the valvebe reliable as a small compromise to the seal will allow contaminants tomigrate to the ink tank during long periods of printer inactivity. Thisis difficult when the pressure difference across the valve is very smallas is the case in the upstream ink line. A large pressure differencetends to clamp the movable valve member against the valve seat, therebyassisting the integrity of the seal.

The valve 138 shown in FIGS. 29 and 30 opens and shuts the upstream inkline for each color simultaneously. The valve body 200 defines inletchannels 202 leading from the ink tank (not shown). Outlet channels 67lead to the LCP moulding (not shown). An actuator arm 204 is pivoted tothe valve body so that a multi valve lifter 208 raises the valve stems210 when an actuation force 206 is applied.

FIG. 30 is a partial section view showing a single valve. The valvemember 212 seals against the valve seat 216 under the biasing action ofthe diaphragm 214. The actuation force 206 works against the diaphragmbias to lift the valve stem 210 and unseat the valve member 214.However, the actuator arm 204 is a first class lever so the actuatorforce 206 uses a mechanical advantage to lift the stems 210.

As discussed above, the pressure difference across the valve is smallbut the integrity of the seal against the valve seat 216 is maintainedby the elastically deformed diaphragm 214. The valve body 212 is aresilient material such as polyurethane for fluid tight sealing againstthe valve seat 216. However, the valve stem 210 has a flanged metal pin218 fitted into an axial recess 220. This ensures the valve lifter 208does not simply slip off the end of the stem 210 by compressing the(relatively) soft resilient material of the valve member 212.

The diaphragm 214 has another important advantage in that it increasesthe interior volume of the ink line when the valve opens. The relativelylarge surface area of the diaphragm 214 creates suction in the ink lineas it lifts up to unseat the valve member 216. As discussed above,creating some suction in the upstream ink line will assist the ink tankto drop to the pressure where the bubble point regulator (see FIG. 24)controls the negative pressure at the printhead ICs.

While lifting the diaphragm drops the hydrostatic pressure in the inkline, lowering the diaphragm too quickly when the valve closes cancreate a pressure spike. This is undesirable as it can cause flooding onthe nozzle plate of the printhead ICs, particularly if the peristalticpump is in the closed condition. However, closing the valve slowlyavoids sending a pulse through the ink line. The reduction in theinternal volume caused by lowering the diaphragm is absorbed by raisingthe level in the ink tank. In view of this, the actuator should open thevalve faster than it closes the valve. A solenoid with damped returnstroke may be used. Another simple actuator uses a shape memory alloy. Ashape memory alloy, such as Nitinol™ wire, tends to inherently damp itsreturn stroke. A heating current drive the initial martensitic toaustenitic phase change, but it reverts to martensite by conductivecooling which tends to be slower. This slow phase change can be usedavoid pressure pulses at the printhead ICs.

The invention has been described herein by way of example only. Skilledworkers in this field will readily recognize many variations andmodifications which do not depart from the spirit and scope of the broadinventive concept.

We claim:
 1. A printhead assembly for installation in an inkjet printer,the printhead assembly comprising: a printhead integrated circuit (IC)having an array of nozzles each with respective actuators for ejectingdrops of ink onto print media; an upstream ink line in fluidcommunication with the printhead IC, the upstream ink line beingconfigured for releasable engagement with an ink supply; a downstreamink line in fluid communication with the printhead IC; a waste inkoutlet in fluid communication with the printhead IC via the downstreamink line; an upstream shut off valve in the upstream ink line; and, adownstream pump mechanism in the downstream ink line.
 2. A printheadassembly according to claim 1 wherein the pump mechanism is reversiblefor pumping ink toward the waste ink outlet or toward the printhead IC.3. A printhead assembly according to claim 2 wherein the pump mechanismis a peristaltic pump.
 4. A printhead assembly according to claim 1wherein the ink supply is an ink cartridge and the upstream ink line isconfigured for releasable sealed fluid engagement with an outlet on theink cartridge.
 5. A printhead assembly according to claim 1 wherein theshut off valve is biased shut and returns to its shut position when theprinthead assembly is installed in the printer and the printer ispowered down.
 6. A printhead assembly according to claim 5 wherein theshut off valve displaces ink when moving to its shut position such thatwhen the shut off valves opens, a finite volume of ink is drawn awayfrom the ink cartridge to drop the hydrostatic pressure at the outlet ofthe ink cartridge.
 7. A printhead assembly according to claim 1 furthercomprising a capper that is movable between an unsealed position spacedfrom the nozzles of the printhead IC and a sealed position creating anair tight seal over the nozzles.
 8. A printhead assembly according toclaim 7 wherein the array of nozzles is formed in a nozzle plate and thecapper is configured to remove ink and particulates deposited on thenozzle plate.
 9. A printhead assembly according to claim 1 furthercomprising a sensor downstream of the printhead IC for sensing thepresence or absence of ink.
 10. A printhead assembly according to claim9 wherein the sensor is upstream of the peristaltic pump.
 11. Aprinthead assembly according to claim 3 further comprising a pluralityof the ink tanks for separate ink colors, and a plurality of upstreamink lines and downstream ink lines for each colour respectively, whereinthe peristaltic pump is a multi-channel peristaltic pump that can pumpeach ink color simultaneously.
 12. A printhead assembly according toclaim 10 further comprising a controller operatively linked to thesensor and the peristaltic pump such that the controller operates thepump in response to output from the sensor.
 13. A printhead assemblyaccording to claim 1 wherein during use, the waste ink outlet is at aless elevated position than the printhead IC.